In an NMR spectrometer, a sample is placed in a static magnetic field which causes atomic nuclei within the sample to align in the direction of the field. Transmit and receive coils, which may be combined in a single coil or set of coils, are placed in the probe positioned close to the sample. The transmit coils apply an RF magnetic field orthogonal to the direction of the static magnetic field, perturbing the alignment of the nuclei. The transmit signal is then turned off, and the resonant RF signal of the sample is detected by the receiver coil. The sensitivity of the spectrometer depends on a number of factors, including the strength of the static field, the closeness of the coupling between the RF coils and the sample, and the resistance of the RF coil.
Currently, most commercial NMR spectrometers use RF coils made of a normal metal, such as copper, or a combination of normal metals. Much research has been devoted to the design of coils for maximum sensitivity. For example, to achieve close coupling, coils have been made that include configurations such as solenoids, saddle coils and birdcage coils, all of which have high filling factors. In each case, however, the resistance of these coil materials has limited their sensitivity. Cooling of RF coils has been suggested to reduce their resistance and minimize thermal noise. However, even when cooled, the sensitivity of conventional normal-metal coils is still limited by their resistance. The use of superconductors in place of conventional normal metal for RF coils in NMR spectrometers has also previously been suggested. For example, U.S. Pat. No. 5,247,256 to Marek describes several RF receiver coil arrangements for NMR spectrometers using thin-film superconducting coils.
In certain analytical environments, it is desirable to test numerous samples as part of an overall experiment. It is also useful to allow an analysis system to be linked to other processes in so-called “hyphenated techniques.” For example, such a system might link a separation technique, such as liquid chromatography, with an analytical technique, such as NMR. Automation in such systems could allow the automatic processing of all the samples needed for the experiment.